The present disclosure relates to a solid-state image pickup device, an electronic apparatus, and a manufacturing method, and more specifically to a solid-state image pickup device in which the sensitivity characteristics for each color are optimized using microlenses that are formed in a novel shape control method, to an electronic apparatus that includes such a solid-state image pickup device, and to a method of manufacturing such a solid-state image pickup device.
Recently, in a solid-state image pickup device, such as a CCD (Charge Coupled Device) sensor and a CMOS (Complementary Metal Oxide Semiconductor) sensor, a microlens has been typically formed for each pixel to improve the sensitivity characteristics. Japanese Unexamined Patent Application Publication No. H04-012568 and No. H10-148704 disclose main methods for forming the microlens.
Japanese Unexamined Patent Application Publication No. H04-012568 discloses a thermal melt flow method that is a technique for forming microlenses by forming a pattern of a microlens material made of a photosensitive resin in a photolithographic method and subsequently performing a thermal reflow of the patterned microlens material.
Japanese Unexamined Patent Application Publication No. H10-148704 discloses a dry-etching transfer method that is a technique for forming microlenses by performing an etching transfer of a photoresist mask material on a microlens material that is formed on a foundation layer of the photoresist mask material. According to the technology disclosed in Japanese Unexamined Patent Application Publication No. H10-148704, it is possible to enlarge the effective area of a microlens by reducing a gap between microlenses of adjacent pixels in a manner of optimizing various conditions for etching requirements by the use of fluorocarbon-based etching gas.
Meanwhile, in the technology disclosed in Japanese Unexamined Patent Application Publication No. H04-012568, if microlenses between adjacent pixels would make in contact with one another, a pattern of microlenses could break down due to thermal fusion. Therefore, it is necessary to form microlenses with a gap between microlenses of adjacent pixels left, which makes it difficult to improve the sensitivity of a solid-state image pickup device.
On the other hand, in the technology disclosed in Japanese Unexamined Patent Application Publication No. H10-148704, it is possible to form microlenses in such a manner that a gap between microlenses of adjacent pixels is not generated in effect by an etchback. In Japanese Unexamined Patent Application Publication No. H10-148704, however, no consideration is given to the optimization of the sensitivity characteristics for each color in a solid-state image pickup device having RGB color pixels. The same is true for Japanese Unexamined Patent Application Publication No. H04-012568.
On the contrary, Japanese Unexamined Patent Application Publication No. 2009-198547 proposes a technology of combining the above-described thermal melt flow method and dry-etching transfer method to improve the sensitivity characteristics for each color in a solid-state image pickup device having RGB color pixels.
In other words, the technology disclosed in Japanese Unexamined Patent Application Publication No. 2009-198547 combines a step of forming a microlens pattern in twice using a photosensitive resin in the thermal reflow method and a step of transferring a shape of the microlens pattern on a transparent resin layer in the dry-etching method using the microlens pattern as an etching mask. This improves the optical transmittance and light concentration performance of the microlenses, thereby allowing to raise the sensitivity of each pixel.
That is, in the technology disclosed in Japanese Unexamined Patent Application Publication No. 2009-198547, in forming a microlens pattern in twice using a photosensitive resin, the microlenses are formed in a manner of dealing with a green pixel in a Bayer array at a first formation time and dealing with red and blue pixels in a second formation time. Subsequently, a pattern of such microlenses is transferred on a transparent resin by performing dry-etching.
Here, in order to optimize the sensitivity characteristics for each color in a solid-state image pickup device having RGB color pixels, it is necessary to consider wavelength dispersion of optical refractive index so as to form a microlens pattern that is optimized for each pixel.
In the technology disclosed in Japanese Unexamined Patent Application Publication No. 2009-198547, however, microlenses to be formed corresponding to the respective red and blue pixels are formed in a microlens pattern having the same shape as one another. Therefore, such a microlens pattern is not optimized for a solid-state image pickup device having RGB color pixels.